Electron diffraction methods for the analysis of silicon carbide surfaces and the controlled growth of polytype heterostructures

Abstract

The growth of different silicon carbide (SiC) polytypes on each other is possible by control of the surface structure and the appropriate thermodynamic parameters. Special ultrahigh vacuum conditions, like those used in solid source molecular beam epitaxy, allow the determination of the species on the surface and also the in situ characterization of the growing polytype by electron diffraction methods. The surface reconstruction which favours the growth of a certain polytype can be controlled by reflection high energy electron diffraction. For a non-destructive determination of the polytype of a grown thin SiC film, methods like x-ray photoelectron diffraction (XPD) and electron channelling can be used. The interaction length of electrons near 1 keV kinetic energy is in the range of 1 nm and therefore sensitive to the stacking sequence of the most common SiC polytypes 3C, 4H, 6H with c-axis dimensions between 0.75 and 1.5 nm. To prepare polytype heterostructures like 4H/3C/4H or 6H/3C/6H, untwinned 3C SiC films without double-positioning boundaries have to be grown. On-axis α-SiC substrates with uniform surface stacking termination are a prerequisite for this. Such surfaces can be prepared using high temperature hydrogen etching, sublimation etching or step-flow growth. These equally terminated crystals with threefold surface symmetry are particularly suitable for detailed studies of the atomic-geometric structure and their changes during growth or after certain treatments. Results of surface-sensitive characterization methods like scanning tunnelling microscopy, XPD and low energy electron diffraction are presented.

Many-beam dynamical simulation of electron backscatter diffraction patterns

“…The reciprocity principle allows us to use the framework of previous ECP simulations also for EBSD [20,21]. A Bloch wave approach is used to describe the diffraction of electrons with wavevector k 0 .…”

“…Because of strong dynamical interactions near a zone-axis, it is very important that our approach can reproduce the rather complicated intensity distribution near a zone axis. These intensities also show a pronounced energy dependence, even to the extent that they can be used as a fingerprint in identification of crystallographic phases [20,21].…”

Polarity determination and control of SiC grown on Si

“…Therefore, to corroborate the hypothesis of different crystallographic polarities of the 3C-SiC(1 1 1) epitaxial layer grown on Si(1 1 1) carbonized under SSMBE and RTCVD conditions XPD measurements were conducted. For single crystals the photoelectron signals show strong intensity modulation as a function of the emission angle, because the photoelectron signal intensity depends on the relative geometric location of all emitters and scatterers as well as on their atomic environment [25,26]. Due to the observed strong element dependence of the XPD spectra in the case of SiC the crystallographic polarity of the surface, being either C-face (3C-SiC(111)) or Si-face (3C- Si(1 1 1)) in the case of SiC(1 1 1) [25,26], or the termination of the 3C-SiC(1 0 0) [39] can be determined.…”

“…For single crystals the photoelectron signals show strong intensity modulation as a function of the emission angle, because the photoelectron signal intensity depends on the relative geometric location of all emitters and scatterers as well as on their atomic environment [25,26]. Due to the observed strong element dependence of the XPD spectra in the case of SiC the crystallographic polarity of the surface, being either C-face (3C-SiC(111)) or Si-face (3C- Si(1 1 1)) in the case of SiC(1 1 1) [25,26], or the termination of the 3C-SiC(1 0 0) [39] can be determined. The polarity of the epitaxial layers grown on differently prepared pseudosubstrates can be determined by measuring the Si 2p/C 1s photoelectron intensity ratio along {1 1 1} directions, i.e.…”

“…The last group consists of electron and ion spectroscopical methods. For example, Auger electron spectroscopy [22,23], X-ray photoelectron spectroscopy [24] and X-ray photoelectron diffraction (XPD) [25,26], electron energy loss spectroscopy [27], Rutherford backscattering [28], coaxial impact collision scattering spectroscopy [29], proton induced X-ray emission [30], time-of-flight mass spectroscopy of recoiled ions and direct recoiled spectroscopy [31] and other methods.…”